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9/8/98 AC 43.13-1B 7-122. GENERAL. The word safetying is a term universally used in the aircraft industry. Briefly, safetying is defined as: “Securing by various means any nut, bolt, turnbuckle etc., on the aircraft so that vibration will not cause it to loosen during operation.” These practices are not a means of obtaining or maintaining torque, rather a safety device to prevent the disengagement of screws, nuts, bolts, snap rings, oil caps, drain cocks, valves, and parts. Three basic methods are used in safetying; safety-wire, cotter pins, and self-locking nuts. Retainer washers and pal nuts are also some- times used. a. Wire, either soft brass or steel is used on cylinder studs, control cable turnbuckles, and engine accessory attaching bolts. b. Cotter pins are used on aircraft and engine controls, landing gear, and tailwheel as- semblies, or any other point where a turning or actuating movement takes place. c. Self-locking nuts are used in applica- tions where they will not be removed often. Repeated removal and installation will cause the self-locking nut to lose its locking feature. They should be replaced when they are no longer capable of maintaining the minimum prevailing torque. (See table 7-2.) d. Pal or speed nuts include designs which force the nut thread against the bolt or screw thread when tightened. These nuts should never be reused and should be replaced with new ones when removed. 7-123. SAFETY WIRE. Do not use stain- less steel, monel, carbon steel, or aluminum alloy safety wire to secure emergency mecha- nisms such as switch handles, guards covering handles used on exits, fire extinguishers, emergency gear releases, or other emergency equipment. Some existing structural equip- ment or safety-of-flight emergency devices re- quire copper or brass safety wire (.020 inch di- ameter only). Where successful emergency operation of this equipment is dependent on shearing or breaking of the safety wire, par- ticular care should be used to ensure that safe- tying does not prevent emergency operation. a. There are two methods of safety wiring; the double-twist method that is most commonly used, and the single-wire method used on screws, bolts, and/or nuts in a closely- spaced or closed-geometrical pattern such as a triangle, square, rectangle, or circle. The sin- gle-wire method may also be used on parts in electrical systems and in places that are diffi- cult to reach. (See figures 7-3 and 7-3a.) b. When using double-twist method of safety wiring, .032 inch minimum diameter wire should be used on parts that have a hole diameter larger than .045 inch. Safety wire of .020 inch diameter (double strand) may be used on parts having a nominal hole diameter between .045 and .062 inch with a spacing between parts of less than 2 inches. When using the single-wire method, the largest size wire that the hole will accommodate should be used. Copper wire (.020 inch diameter), alu- minum wire (.031 inch diameter), or other similar wire called for in specific technical or- ders, should be used as seals on equipment such as first-aid kits, portable fire extinguish- ers, emergency valves, or oxygen regulators. CAUTION: Care should be taken not to confuse steel with aluminum wire. c. A secure seal indicates that the com- ponent has not been opened. Some emergency devices require installation of brass or soft Par 7-122 Page 7-19 SECTION 7. SAFETYINGPDF Image | AFS-640
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